Frontotemporal lobar degeneration (FTLD) is the second most common cause of dementia affecting individuals younger than 65 years; see, e.g., McKhann et al., Arch. Neurol. 58 (2001), 1803; Forman et al., Ann. Neurol. 59 (2006), 952-62. On a cellular pathologic level, the characteristic lesions in the majority of FTLD brains are abnormal ubiquitinated protein inclusions. The biochemical composition of the ubiquitinated inclusions in the most common pathological form of FTLD, namely FTLD-U, remained unknown until 2006, when the TAR-DNA binding protein 43 (TDP-43) was identified as the major disease protein in the majority of sporadic and familial FTLD-U cases. Subsequently, the ubiquitinated compact inclusions, characteristic for amyotrophic lateral sclerosis (ALS) were also found to be composed of TDP-43, thereby providing evidence that both conditions are mechanistically linked and part of spectrum of diseases which can be classified as TDP-43 proteinopathies, see, e.g., Neumann et al., Science 314 (2006), 130-133.
Other than FTLD and ALS, TDP-43 is also known to accumulate in the nerve cells and glial cells of ALS-Parkinsonism dementia complex of Guam, corticobasal degeneration, Dementia with Lewy bodies, Huntington's disease, Lewy body disease, motor neuron disease, frontotemporal dementia, frontotemporal lobar degeneration with ubiquitin-positive inclusions, hippocampal sclerosis, inclusion body myopathy, inclusion body myositis, Parkinson's disease, Parkinson's disease dementia, Parkinson-dementia complex in Kii peninsula and Pick's disease and the like; see e.g., Lagier-Tourenne et al., Hum. Mol. Gen. 19 (2010), R46-64, which is herein incorporated by reference in its entirety. These diseases are collectively referred to as TDP-43 proteinopathies. Abnormal accumulation of TDP-43 is observed at the site of lesions of each disease which appears to imply involvement in the cause of nerve degeneration in these diseases. Increased cytoplasmic localization of TDP-43 in brains and spinal cords of patients termed as “pre-inclusions” has been proposed to be an early event in TDP-43 proteinopathies, with the implication of a possible pathogenic role in these diseases; see, e.g. Giordano et al., Brain Pathol, 20 (2010), 351-60, Consistently, increased cytoplasmic TDP-43 localization at presymptomatic stages has been reported to be found in mice overexpressing wild type TDP-43; see e.g., Wils et al., Proc. Natl Acad. Sci. USA 107 (2010), 3858-63 as well as in an acute rat model with adenovirus-mediated wild-type TDP-43 expression; see, e.g., Tatom et al., Mol. Ther. 17 (2009), 607-613. Commercially available monoclonal murine antibodies are primarily used in the studies on TDP-43 and to conduct pathological diagnosis of TDP-43 proteinopathies. A monoclonal murine anti-TDP-43 antibody, which recognizes the phosphorylated form of TDP-43 is disclosed in European Patent Application No. 2 189 526 A1. Additional anti-TDP-43 antibodies are disclosed in Mang et al., Proc Natl Acad Sci USA, 106(18):7607-12 (2009) and U.S. Patent Application Pub. No. 20100136573.
The success in generating monoclonal antibodies rests among other things, on the efficient and selective fusion of antigen-stimulated B cells with a murine myeloma cell line followed by selection of stable antibody producing hybrids as originally described by Kóhler and Milstein, Nature 256 (1975), 495-497. However, the therapeutic utility of murine based antibodies in human is hampered by the human anti-mouse antibody (HAMA) response as a consequence of their non-human origin. Approaches for making human or human-like monoclonal antibodies became available through genetic engineering. However, these methods typically suffer from the drawback that they are not suitable for producing antibodies displaying many of the characteristics of antibodies that are endogenously produced by the human immune system during the course of a physiological human immune response. Furthermore these genetically engineered antibodies may show undesired cross-reactivity with other proteins and/or the target protein in the context of the biologically relevant native conformation and normal physiological function of the target antigen. The resulting side effects upon systemic administration of the exogenous antibodies may range from for example, undesired autoimmune disease to anaphylactic reactions. These side effects have been reported in so-called “humanized antibodies,” which originally stem from non-human organisms, such as mice, as well as so called “fully human antibodies,” in vitro or in xenogeneic mice genetically engineered to express a repertoire of human antibodies. On the other hand, active immunization with pathologically relevant antigens bears the considerable risk of patients developing uncontrollable immune responses against these antigens and cross-reactivity with endogenous antigens that may consequently lead to dangerous autoimmune responses.
Furthermore, the development of assays to detect and monitor levels of normal and pathological TDP-43 in plasma, cerebrospinal fluid, and other samples as biomarkers of FTLD and ALS will provide the ability to diagnose and distinguish TDP-43 proteinopathies from other clinically similar neurodegenerative disorders, such as tauopathies or related proteinopathies. In addition, the development of imaging ligands that enable the detection and/or quantification of TDP-43 neuropathology in living patients will provide a powerful tool not only for diagnosis, but also for monitoring the response of patients having a neurodegenerative TDP-43 proteinopathy to disease-modifying therapies when they become available.
Thus, there is a need to overcome the above-described limitations and to provide therapeutic and diagnostic antibodies and other binding molecules that specifically recognizes biologically relevant conformations of TDP-43.